I have implemented the Euler symplectic method using repa. It is a pretty simple method. Sadly the performance I am getting is not as good as I would have hoped. The repa guys have been very helpful (Ben Lippmeier in particular) and I have followed his advice on inlining and adding strictness annotations. Unfortunately these do not seem to have helped. I am producing the core with
ghc --make -O2 RepaOnly.hs -main-is RepaOnly -ddump-prep -dsuppress-all -dppr-case-as-let -dppr-cols200 > RepaOnly.hcr
Sadly this seems to be quite large and I am currently not sure how to proceed. I thought the wider Haskell community might have some ideas on how to debug this or point out where I am going wrong.
The code is here: https://gist.github.com/idontgetoutmuch/6209752
I can also post the core in a gist if that is helpful.